A method has been developed by the Applicants for preparing straight chain saturated or unsaturated aliphatic .alpha., .omega. -diamines containing from 8 to 12 carbon atoms, by reductive amination of the corresponding .alpha., .omega. -dialdehydes.
More particularly, the subject matter of the study by the Applicants is characterized in that the .alpha., .omega. -dialdehyde is first converted into the corresponding diimine by low temperature reaction in an aqueous mixture of an organic solvent with ammonia, and that the diimine thus obtained is then subjected to reaction with hydrogen in the presence of a catalyst which, under the reaction conditions, is effective to reduce all the double imino bonds, while leaving the olefin bonds, if any, unaltered, and in the event of olefin bonds being present and a saturated .alpha., .omega. -diamine being the desired product, the resulting unsaturated diamine is subjected to hydrogenation in the presence of a catalyst selected from palladium, platinum, ruthenium, and rhodium.
Thus, in accordance with that study, starting from unsaturated dialdehydes, there can be obtained both the corresponding unsaturated diamines and the saturated ones, while from the saturated dialdehydes the corresponding saturated diamines are obtained.
For use as an organic solvent in the aqueous mixture, wherein the .alpha., .omega. -dialdehyde is reacted with ammonia, an alcohol is indicated, preferably ethyl alcohol, dioxane, or tetrahydrofuran.